The present invention relates to a process for producing a lubricating base oil or insulating oil from a mineral oil, a mixture of a mineral oil and a long-chain alkylbenzene or the like. In particular, the present invention relates to a process for producing a markedly low pour point oil by separating a lighter fraction by distillation after hydrodewaxing treatment.
The insulating oil, lubricating oil and the like are required to have fluidity at low temperatures, because they are sometimes used in a cold district. For example, the pour point of the insulating oil is specified at not higher than xe2x88x9227.5xc2x0 C. as the first-class No. 2 of JIS C2320 and not higher than xe2x88x9245xc2x0 C. as Class II of IEC 296.
To secure a low-temperature fluidity, it is necessary to use a wax-free oil, because the wax precipitates at low temperatures. Conventionally, the base oil was produced using as a raw material a naphthene crude oil having a small wax content. The naphthene crude oil is available only from a limited district and is therefore exhausted so that the use of it is disadvantageous in cost. Under such situations, a paraffin crude oil is replaced for the naphthene crude oil, but it requires a wax removal step, that is, dewaxing in advance. For dewaxing, adopted is a solvent dewaxing method wherein the wax precipitated by diluting the paraffin crude oil with a solvent such as methyl ethyl ketone/toluene or the like and then cooling is removed by filtration or a hydrodewaxing method wherein the wax is decomposed and removed by a form-selective zeolite catalyst.
The solvent dewaxing method needs much energy for cooling and removal of the solvent. Particularly when an oil having a pour point not higher than xe2x88x9220xc2x0 C. is desired, it is necessary to lower the cooling temperature correspondingly. The solvent dewaxing treatment tends to be accompanied with the coloring of an insulating oil so that activated clay treatment for the removal of the color is necessary. Owing to the difficulty in the regeneration of the activated clay after the treatment, it must be disposed as an industrial waste. Under such circumstances, a simple hydrodewaxing method which permits dewaxing at a low cost has attracted attentions.
With regards to the production of an insulating oil by hydrodewaxing, a method which comprises obtaining a raffinate by subjecting a fraction of 232 to 566xc2x0 C. to solvent extraction, hydrodewaxing the raffinate at 260 to 358xc2x0 C. and hydro-refining the resulting raffinate at 218 to 316xc2x0 C. is described in U.S. Pat. No. 4,137,148 which corresponds to JP-A54-22413 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent application). It says that by this method, a base oil having a pour point not higher than xe2x88x9234.4xc2x0 C. can be manufactured.
Although the hydrodewaxing treatment is suited for the production of a low pour point oil at a low cost, severer conditions are necessary for producing an oil having a pour point not higher than xe2x88x9235xc2x0 C. Particularly, the production of an oil having a pour point not higher than xe2x88x9240xc2x0 C. requires markedly severe treatment conditions and in addition, is accompanied with such a problem of a reduction in the yield of the oil.
An object of the present invention is to provide a process for producing a low pour point oil which is free of the above-described problems. Specifically, an object of the present invention is to provide a process which permits the production of a low pour point oil without severer hydrodewaxing treatment conditions.
The present inventors have proceeded with various investigations with a view to overcoming the above-described problems. As a result, it has been found that a lighter fraction of the hydrodewaxed mineral oil has a pour point lower than the heavy fraction. As a result of a further investigation, it has also been found that a lower pour point oil can be produced easily by using a fraction up to the point of 80% distillation, leading to the completion of the present invention.
The process for producing the oil according to the present invention principally comprises a step of separating from a crude oil a fraction having a boiling point ranging from 250 to 600xc2x0 C. by distillation; a step of hydrodewaxing the resulting fraction at a temperature range of from 250 to 500xc2x0 C. in the presence of a zeolite catalyst; a step of removing a fraction having a boiling point not lower than 230xc2x0 C. but not higher than 250xc2x0 C.; and a step of separating a lighter fraction up to the point of 80% distillation by distillation.
Since the oil available by the above-described process only is sometimes accompanied with the coloring problem, a hue improving treatment is carried out as needed. For the improvement of the hue, there are two methods; one is the treatment with a solid adsorbent by using, for example, activated clay and the other one is hydrogenating treatment in the presence of a hydro-refining catalyst. The hydro-refining treatment is preferred because the use of activated clay or the like is accompanied with such a problem as the treatment of the adsorbent after use. In the present invention, the hydrodewaxing treatment step is essential so that when a hydro-refining treatment is carried out, the dewaxed mineral oil can be fed continuously to the hydro-refining treatment step as is or after separated by distillation. In this respect, the hydro-refining treatment is preferred.
The production process which has the hydro-refining treatment step added thereto comprises hydrodewaxing a mineral oil fraction, which has been separated from a crude oil by distillation and has a boiling point ranging from 250 to 600xc2x0 C., at a temperature range of from 250xc2x0 C. to 500xc2x0 C. in the presence of a zeolite catalyst; hydrogenating the hydrodewaxed fraction at 320 to 380xc2x0 C. in the presence of a hydro-refining catalyst; and separating a lighter fraction by distillation. The hydrodewaxed oil may be fed to the hydro-refining treatment step as is or after separated by distillation. This method is suited for the case where the hydro-refining of a heavy fraction is not necessary.
If a nitrogen content in the raw material oil is high and the activity of the zeolite catalyst shows a marked deterioration or if long-term continuous use of the zeolite catalyst is desired, the hydrodewaxing treatment may follow the hydro-refining treatment. Described specifically, such a method comprises hydrogenating a mineral oil fraction, which has been separated from a crude oil by distillation and has a boiling point ranging from 250 to 600xc2x0 C., at a temperature range of from 320xc2x0 C. to 380xc2x0 C. in the presence of a hydro-refining catalyst; hydrodewaxing the resulting fraction at a temperature range of from 250xc2x0 C. to 500xc2x0 C. in the presence of a zeolite catalyst; subjecting the hydrodewaxed fraction to hue improving treatment at a temperature range of from 250 to 350xc2x0 C. in the presence of a hydro-refining catalyst; and separating a lighter fraction by distillation. After the hydrodewaxing treatment, the hydro-refining treatment is carried out at a temperature of 250 to 350xc2x0 C. for the improvement of the hue. As described above, the hydrodewaxed oil may be fed to the hydro-refining treatment step as is or after separated by distillation.
The process for producing the insulating oil of the present invention will next be described more specifically.
Starting material
As a starting material, a mineral oil which is a fraction separated from a crude oil by distillation and having a boiling point ranging from 250 to 600xc2x0 C. (in terms of normal pressure) and a viscosity of about 5 to 20 mm2/s (40xc2x0 C.) is preferably employed. The mineral oil subjected to solvent extraction as needed and having a viscosity of 50 to 300 mm2/s (40xc2x0 C.) can also be employed.
Preparation of a refined mineral oil
The above-described mineral oil fraction is hydrodewaxed at 250 to 500xc2x0 C. in the presence of a zeolite catalyst. As the hydrodewaxing catalyst, preferred are those obtained by adding a binder to the main component zeolite, for example, pentasil type zeolite, ferrierite or mordenite, which has a silica-alumina ratio of 20:500, and then forming or molding the resulting mixture. Although the hydrodewaxing conditions cannot be determined in a wholesale manner because they are influenced by various factors, the following conditions are usually employed: a temperature of 250 to 500xc2x0 C., preferably 350 to 450xc2x0 C., a hydrogen partial pressure of 3.0xc3x97106 to 1.5 xc3x97107 Pa (about 30 to 150 kgf/cm2 in terms of gauge pressure), preferably 6.0xc3x97106 to 9.8xc3x97106 Pa (about 60 to 100 kgf/cm2 in terms of gauge pressure), a liquid hourly space velocity (LHSV) of 0.2 to 2.0 hxe2x88x921 and a hydrogen/oil volume ratio of 300 to 3000 l/l, preferably 500 to 1500 l/l. At temperatures lower than 250xc2x0 C., the hydrodewaxing treatment happens to be incomplete. Temperatures exceeding 500xc2x0 C., on the other hand, happens to accelerate the decomposition and are therefore not preferred. Anyway, the conditions should be selected so as to finally satisfy a predetermined pour point.
Then, the hydrodewaxed mineral oil fraction is hydrogenated, as is or after separated by distillation into a fraction having a boiling point ranging from 250 to 600xc2x0 C. (in terms of normal pressure), at a temperature range of 320 to 380xc2x0 C. in the presence of a hydro-refining catalyst. If the apparatus is designed to carry out the hydrodewaxing and hydro-refining treatments successively, it is preferred that the hydrodewaxed mineral oil is subjected to hydro-refining treatment as is. The distillation operation inserted after the hydrodewaxing treatment sometimes causes a coloring problem due to thermal treatment. Alternatively, the hydro-refining treatment may be carried out after the separation of the hydrodewaxed oil by distillation. The latter method is suited when the hydro-refining treatment of a heavy fraction is unnecessary.
Examples of the hydro-refining catalyst include those having one or more metals selected from Ni, Co, Mo, W and the like supported on a carrier of silica, alumina or silica-alumina. Although the hydro-refining conditions cannot be determined in a wholesale manner because they are influenced by various factors, the following conditions are usually employed: a temperature of 320 to 380xc2x0 C., a hydrogen partial pressure of 4.5xc3x97106 to 1.2xc3x97107 Pa (about 45 to 120 kgf/cm2 in terms of gauge pressure), preferably 6.0xc3x97106 to 9.9xc3x97106 Pa (about 60 to 100 kgf/cm2 in terms of gauge pressure) and LHSV of 0.2 to 2.0 hxe2x88x921. At temperatures lower than 320xc2x0 C., the hydro-refining treatment happens to be incomplete. Temperatures exceeding 380xc2x0 C., on the other hand, happens to accelerate the decomposition and are therefore not preferred. Furthermore, the conditions should be set so that the desulfurization ratio will preferably become at least 95%, more preferably at least 98%; the denitrification ratio will preferably become at least 95%, more preferably at least 98%; and the decomposition ratio will become 5% or lower.
After the hydrogenation treatment, it is possible to carry out solvent extraction refining as needed under the conditions of a raffinate yield of 60 to 90 vol. % by using a solvent which selectively extracts an aromatic hydrocarbon.
As described above, the hydrodewaxing treatment and hydro-refining treatment can be carried out in the reverse order. Particularly in the case where the mineral oil fraction has an extremely high nitrogen content and the activity of a hydrodewaxing catalyst is apt to lower, the reverse order is preferred. The reverse order makes it possible to reduce the catalyst regeneration frequency. When the hydro-refining treatment is carried out in advance, the nitrogen content is reduced which permits the hydrodewaxing treatment at a relatively low temperature. Specifically, the hydrodewaxing temperature can be lowered by about 50xc2x0 C. compared with the treatment without the preliminary hydro-refining treatment. The mineral oil after the hydrodewaxing treatment however has poor hue so that the hue improving treatment is required. The hue improving treatment is carried out at 250 to 350xc2x0 C. in the presence of a hydro-refining catalyst. Treatment temperatures lower than 250xc2x0 C. sometimes fail to complete the hue improving treatment. Temperatures exceeding 350xc2x0 C., on the other hand, happen to accelerate the decomposition reaction. Temperatures outside the above range are therefore not preferred.
It is also possible to carry out the hue improving treatment by hydro-refining after the separation of the hydrodewaxed oil by distillation. The refined mineral oil is, similar to the above-described treatment, subjected to solvent extraction refining as needed under the conditions of a raffinate yield of 60 to 90 vol. % beta solvent which selectively extracts an aromatic hydrocarbon.
Production of a low pour point oil
From the refined mineral oil so obtained, the heavy fraction is removed, because the hydrodewaxing treatment effectively acts on the wax content of a lighter fraction and in comparison, the dewaxing of the heavy fraction does not proceed smoothly. The pour point of the lighter fraction shows a drastic decrease, while that of the heavy fraction becomes relatively high. As the lighter fraction, that up to the point of 80% distillation, preferably 70% distillation, more preferably 66% distillation are subjected to fractional distillation. Inclusion of the lighter fraction other than that up to the point of 80% distillation causes a drastic increase in the pour point and is therefore not preferred.
Upon fractional distillation, the fraction of 240xc2x0 C. or lower contained, if any, in the refined mineral oil is removed by stripping. It does not matter whether the fractional distillation and stripping are carried out simultaneously. When a long-chain alkylbenzene is added, it is added in an amount of 10 to 40 parts by weight.